Vlsi report using latex

AMITY UNIVERSITY
Rajasthan
VLSI LAB REPORT
SUBMITTED TO
Mr.Venkatrao Selamneni
SUBMITTED BY
Priya Hada
B.tech(ECE)6th
sem
April 28, 2014

Contents
1 INTRODUCTION TO VLSI 1
2 EXPERIMENT NO.1(a) 3
3 EXPERIMENT NO.1(b) 6
4 EXPERIMENT NO.2 10
i

List of Figures
1 Schematic of NMOS . . . . . . . . . . . . . . . . . . . . . . . 4
2 Waveform of NMOS . . . . . . . . . . . . . . . . . . . . . . . 5
3 Schematic of PMOS . . . . . . . . . . . . . . . . . . . . . . . 8
4 Waveform of PMOS . . . . . . . . . . . . . . . . . . . . . . . 9
5 Inverter truth table . . . . . . . . . . . . . . . . . . . . . . . . . 10
6 CMOS inverter . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7 DC characteristics of CMOS inverter . . . . . . . . . . . . . . . 11
8 Schematic of CMOS inverter . . . . . . . . . . . . . . . . . . . 12
9 DC characteristic waveform of CMOS inverter . . . . . . . . . 13
10 Transient characteristics of CMOS inverter with pulse input. . . 14
12 Waveform of CMOS inverter . . . . . . . . . . . . . . . . . . . 16
13 propagation delay graph . . . . . . . . . . . . . . . . . . . . . 17
15 Waveform of CMOS inverter . . . . . . . . . . . . . . . . . . . 19
16 NOR Gate and its truth table . . . . . . . . . . . . . . . . . . . 20
17 Schematic of NOR Gate . . . . . . . . . . . . . . . . . . . . . 21
18 Symbol of NOR Gate . . . . . . . . . . . . . . . . . . . . . . . 21
19 Waveform of NOR Gate . . . . . . . . . . . . . . . . . . . . . 22
20 NAND gate using CMOS logic and its truth table . . . . . . . . 23
21 Schematic of NAND Gate . . . . . . . . . . . . . . . . . . . . 24
22 Waveform of NAND Gate . . . . . . . . . . . . . . . . . . . . 25
23 XOR Gate and its truth table . . . . . . . . . . . . . . . . . . . 26
24 Schematic of XOR Gate . . . . . . . . . . . . . . . . . . . . . 27
25 Waveform of XOR Gate . . . . . . . . . . . . . . . . . . . . . 28
26 XNOR Gate and its truth table . . . . . . . . . . . . . . . . . . 29
27 Schematic of XNOR Gate . . . . . . . . . . . . . . . . . . . . 30
28 Waveform of XNOR Gate . . . . . . . . . . . . . . . . . . . . 31
29 Two input AND gate with truth table . . . . . . . . . . . . . . . 32
ii

30 AND gate using CMOS . . . . . . . . . . . . . . . . . . . . . 33
31 Schematic of NAND gate . . . . . . . . . . . . . . . . . . . . . 33
32 Schematic of NOT gate . . . . . . . . . . . . . . . . . . . . . . 34
33 Schematic of AND gate . . . . . . . . . . . . . . . . . . . . . . 35
34 SR latch diagram with Function Table . . . . . . . . . . . . . . 36
35 Schematic of NAND Gate . . . . . . . . . . . . . . . . . . . . 37
36 Schematic of Symbol of NAND Gate . . . . . . . . . . . . . . . 37
37 Waveform of NAND Gate . . . . . . . . . . . . . . . . . . . . 38
38 Schematic of SR Latch . . . . . . . . . . . . . . . . . . . . . . 38
39 Waveform of SR latch . . . . . . . . . . . . . . . . . . . . . . . 39
40 Symbol and Truthtable of D flipflop . . . . . . . . . . . . . . . 40
41 Schematic D flipflop . . . . . . . . . . . . . . . . . . . . . . . 41
42 Waveform of D flipflop . . . . . . . . . . . . . . . . . . . . . . 42
iii

1 INTRODUCTION TO VLSI
Very-large-scale integration (VLSI) is the process of creating integrated circuits
by combining thousands of transistors into a single chip. Since the invention
of the first Integrated Circuit(IC) by Jack Kilby in 1958, ability to pack more
and more transistors onto a single chip has been very rapid. In the early 1960s,
low density fabrication processes classified under Small Scale Integration (SSI)
in which transistor count was limited to about 10. This rapidly gave way to
Medium Scale Integration (MSI) later in the decade, when around 100 transis-
tors could be placed on a single chip. Early 1970s saw the growth of transistor
count to about 1000 per chip called the Large Scale Integration (LSI).
By mid-1980, the transistor count on a single chip exceeded 1000 and hence
came the age of Very Large Scale Integration or VLSI, which is large scale
integration with a single chip of size as small as 50 millimeters square having
more than a million transistor and circuits in it.
VLSI chiefly comprises of front end design and back end design. While
front end design includes digital design using HDL, design verification through
simulation and other verification techniques, the design from gates and design
for testability, backend design comprises of complementary metal-oxide semi-
conductor (CMOS) design and its characterization.The entire VLSI circuit de-
sign procedure follows a step by step approach, where each design step is fol-
lowed by simulation before it’s put into the hardware. Most VLSI designs are
classified into three Categories:
1. Analog: Small transistor count precision circuits such as Amplifiers, Data
converters, filters, Phase Locked Loops, Sensors etc.
2. Application Specific Integrated Circuits (ASICS): Progress in the fabri-
cation of internal circuits has enabled faster and more powerful circuits in
smaller and smaller devices. ASICS are created for specific purposes and
each device is created to do a particular job, and do it well.
3. Systems on a Chip (SoC): These are highly complex mixed signal circuits,
such as a network processor chip or a wireless radio chip.
Advantages offered by VLSI:
1. Integration improves the design
2. Compactness: less area, physically smaller.
3. Higher speed: lower parasitics(reduced interconnection length).
1

4. Lower power consumption.
5. Higher reliability: improved on-chip interconnects.
6. Integration signiﬁcantly reduces manufacturing cost.
2

2 EXPERIMENT NO.1(a)
AIM
Study the drain and transfer characteristics of NMOS.
SOFTWARE REQUIRED
Design Architect Tool by Mentor Graphics, LINUX operating system.
THEORY
MOSFET is a four terminal device. The voltage applied to the gate terminal de-
termines if and how much current flows between the source and the drain ports.
The body represents the fourth terminal of the transistor. Its function is sec-
ondary as it only serves to modulate the device characteristics and parameters.
In N-type MOSFET (NMOS), the body is of p-type. The drain, the source and
the channel between the two are of n-type.
Working of NMOS
Initially, VGS = 0, i.e. when no gate to source voltage is applied, it is similar
to two diodes connected back to back between the source and the drain. So,
no current flows from source to drain. Also, a depletion layer is formed at the
source-substrate and the drain-substrate junctions. The holes under the gate are
repelled to produce a depletion region and it becomes continuous.
The VGS is then increased above the Threshold Voltage. At this time, minor-
ity carriers in p-type substrate (electrons) cross the depletion region and reaches
under the gate. The process is called surface inversion.
Modes of operation
It has three modes of operation:
1. Cut-off mode: When no current flows through transistor i.e. ID = 0
occurs when
VGS < VTH
Where VGS: gate to source voltage ; VTH: threshold voltage
3

2. Triode Region: It is a linear region in graph which obeys Ohms law. It
occurs when
VGS > VTH
and
VDS < VGS − VTH
The current equation in triode mode is given as:
ID =
W
L
.µn.Cox(VGS − VTH −
VDS
2
).VDS
3. Saturation Mode: When current becomes constant i.e. ID remains con-
stant no matter how much we increase VGS. It occurs when
VGS > VTH
and
VDS > VGS − VTH
The current equation in saturation mode is given as:
ID =
W
2L
.µn.Cox.(VGS − VTH)2
(1 + λp.VDS)
Where : modulation index
Schematic
Figure 1: Schematic of NMOS
4

Waveforms
Figure 2: Waveform of NMOS
Result
In V I characteristics of NMOS, we observe that at constant VGS if the value of
VDS will increase, then the drain current is saturated.
5

3 EXPERIMENT NO.1(b)
AIM
To study the drain and transfer characteristics of PMOS.
SOFTWARE REQUIRED
THEORY
The structure and operation of a PMOS device is essentially the same, except
that wherever there was n-type silicon, there is now p-type silicon. The PMOS
channel is a part of n-type substrate lying between two heavily doped p+ wells
beneath the source and drain.
Working of PMOS
The operation of PMOS is similar to NMOS. To create an inversion layer in the
n-type substrate, holes have to be attracted to the gate. As a result, p-type chan-
nel will induce between drain and source, the voltage VTH must be sufficiently
negative. The VTH is thus negative, so, channel is induced only if VGS < VTH If
we make the voltage VDS sufficiently negative, the p-type induced channel will
pinch-off. When VDS will be negative, the drain current will flow from source
to drain, exactly opposite to that of NMOS device with a positive VDS .
Modes of Operation
It has three modes of operation -
1. Cut-off mode: It is a mode in which channel is not formed and no current
flows through transistor i.e. ID = 0. It occurs when
VGS > VTH
Where VGS: gate to source voltage, VTH: threshold voltage.
6

2. Linear/Triode region: It is a mode in which channel formation takes place
and thus, current ﬂows from source to drain. This region of graph follows
Ohms law due to linear relationship between IDS and VDS. It occurs when
VGS < VTH
and
VDS > VGS − VTH
The current equation in triode mode is given as:
ID = −
W
L
.µn.Cox(VGS − VTH −
VDS
2
).VDS
3. Saturation mode: In this mode the channel pinches off and the VDSat
which the current saturation occurs is called VDSat or pinch-off voltage.
In this mode the PMOS acts similar to current source.ID is independent
of VDS. It occurs when
VGS < VTH
and
VDS < VGS − VTH
The current equation in saturation mode is given as:
ID = −
W
2L
.µn.Cox.(VGS − VTH)2
(1 + λp.VDS)
Where λp: modulation index
7

Schematic
Figure 3: Schematic of PMOS
8

Waveforms
Figure 4: Waveform of PMOS
Result
The characteristics of PMOS are obtained. All the parameters(voltages and
current) are taken in negative side.
9

4 EXPERIMENT NO.2
AIM
To study D.C. analysis of CMOS inverter.
SOFTWARE REQUIRED
THEORY
Figure 5: Inverter truth table
Figure 6: CMOS inverter
The inverter is universally accepted as the most basic logic gate doing a
Boolean operation on a single input variable.As shown, the simple structure
consists of a combination of an PMOS transistor at the top and a NMOS tran-
sistor at the bottom. CMOS is referred to as complementary-symmetry metalox-
idesemiconductor. The words ”complementary-symmetry” refer to the fact that
the typical digital design style with CMOS uses complementary and symmetri-
cal pairs of p-type and n-type metal oxide semiconductor ﬁeld effect transistors
10

(MOSFETs) for logic functions. Two important characteristics of CMOS de-
vices are high noise immunity and low static power consumption. Signiﬁcant
power is only drawn while the transistors in the CMOS device are switching be-
tween on and off states. Consequently, CMOS devices do not produce as much
waste heat as other forms of logic.
DC analysis of CMOS inverter
Figure 7: DC characteristics of CMOS inverter
As shown in above ﬁgure there are 5 regions of operation which are sum-
marized as in the table:
11

Schematic
Figure 8: Schematic of CMOS inverter
12

Waveforms
Figure 9: DC characteristic waveform of CMOS inverter
RESULT
The DC characteristic of CMOS inverter is obtained successfully.
13

5 EXPERIMENT NO.3
AIM
To study transient analysis of CMOS inverter.
SOFTWARE REQUIRED
THEORY
Figure 10: Transient characteristics of CMOS inverter with pulse input.
Transient analysis tells Vout(t) if Vin(t) changes. It requires solving differ-
ential equations. Input is usually considered to be a pulse stream.. It is also
called AC analysis or dynamic analysis or switching analysis.The switching
characteristic (Vout(t) given Vin(t)) of a logic gate tells the speed at which the
gate can operate. The switching speed of a logic gate can be measured in terms
of the time required to charge and discharge a capacitive load. Fig.1 shows the
dynamic characteristics of a CMOS inverter. The following are some formal
deﬁnitions of temporal parameters of digital circuits. All percentages are of the
steady state values.
1. Rise Time (tr) : Time taken to rise from 10% to 90%
14

2. Fall Time (tf ): Time taken to fall from 90% to 10%
3. Edge Rate (trf ): (tr + tf )/2.
4. High-to-Low propagation delay (tpHL): Time taken to fall from VOH to
50%.
5. Low-to-High propagation delay (tpLH): Time taken to rise from 50% to
VOL.
6. Propagation Delay (tp): (tpHL + tpLH)/2.
7. Contamination Delay (tcd): Minimum time from the input crossing 50%
to the output crossing 50%.
Schematic
15

Waveforms
Figure 12: Waveform of CMOS inverter
RESULT
The transient characteristics of the CMOS inverter using pulse input is obtained
successfully.
16

6 EXPERIMENT NO.4
AIM
Calculate Rise time, Fall time and Propagation delay of CMOS inverter.
SOFTWARE REQUIRED
THEORY
There are some basic terms that should be known for calculating the transient
parameters of a CMOS inverter. Those are:
1. Switching speed : limited by time taken to charge and discharge, CL .
2. Rise time, tr: Waveform to rise from 10% to 90% of its steady state value
3. Fall time tf , : 90% to 10% of steady state value
4. Delay time, td : time difference between input transition (50%) and 50%
output level
Figure 13: propagation delay graph
The propagation delay tp of a gate deﬁnes how quickly it responds to a change at
its inputs, it expresses the delay experienced by a signal when passing through
17

a gate. It is measured between the 50% transition points of the input and output
waveforms as shown in the ﬁgure 1 for an inverting gate. The τpLH deﬁnes the
response time of the gate for a low to high output transition, while τpHL refers
to a high to low transition. The propagation delay as the average of the two i.e.
tp =
1
2
(τpLH + τpHL)
Schematic
18

Waveforms
Figure 15: Waveform of CMOS inverter
RESULT
Rise time, Fall time and Propagation delay of CMOS inverter are calculated.
19

AIM
To design two input NOR gate using CMOS logic.
SOFTWARE REQUIRED
THEORY
The NOR gate is a digital logic gate that implements logical NOR. A HIGH
output (1) results if both the inputs to the gate are LOW (0); if one or both input
is HIGH (1), a LOW output (0) results. NOR is the result of the negation of the
OR operator. It can also be seen as an AND gate with all the inputs inverted.
NOR is a functionally complete operationNOR gates can be combined to
generate any other logical function. NOR gates are so-called ”universal gates”
that can be combined to form any other kind of logic gate.
Figure 16: NOR Gate and its truth table
20

Schematic
Figure 17: Schematic of NOR Gate
Symbol
Figure 18: Symbol of NOR Gate
21

Waveforms
Figure 19: Waveform of NOR Gate
RESULT
The wave forms of two input NOR gate are obtained successfully.
22

AIM
To design two input NAND gate using CMOS logic.
SOFTWARE REQUIRED
THEORY
The two-input NAND gate shown in the ﬁgure is built from four transistors. The
series-connection of the two n-channel transistors between GND and the gate-
output ensures that the gate-output is only driven low (logical 0) when both
gate inputs a or b are high (logical 1).The complementary parallel connection
of the two transistors between VCC and gate-output means that the gate-output
is driven high (logical 1) when one or both gate inputs are low (logical 0). The
net result is the logical NAND function.
Figure 20: NAND gate using CMOS logic and its truth table
23

Schematic
Figure 21: Schematic of NAND Gate
24

Waveforms
Figure 22: Waveform of NAND Gate
RESULT
The wave forms of two input NAND gate are obtained successfully.
25

AIM
To design two input XOR gate using CMOS logic.
SOFTWARE REQUIRED
THEORY
output is ”true” if either, but not both, of the inputs are ”true.” The output is
”false” if both inputs are ”false” or if both inputs are ”true.” Another way of
looking at this circuit is to observe that the output is 1 if the inputs are different,
but 0 if the inputs are the same. XOR can also be viewed as addition modulo
2. As a result, XOR gates are used to implement binary addition The XOR
( exclusive-OR ) gate acts in the same way as the logical ”either/or.” The in
computers. The algebraic expressions
A.B + A.B
and
(A + B).A.B
both represent the XOR gate with inputs A and B.
Figure 23: XOR Gate and its truth table
26

Schematic
Figure 24: Schematic of XOR Gate
27

Waveforms
Figure 25: Waveform of XOR Gate
RESULT
The wave forms of two input NAND gate are obtained successfully.
28

AIM
To design two input XNOR gate using CMOS logic.
SOFTWARE REQUIRED
THEORY
The XNOR gate (sometimes spelled ”exnor” or ”enor” and rarely written NXOR)
is a digital logic gate whose function is the inverse of the exclusive OR (XOR)
gate. The XNOR (exclusive-NOR) gate is a combination XOR gate followed
by an inverter.
The two-input version implements logical equality. A HIGH output (1) re-
sults if both of the inputs to the gate are the same. If one but not both inputs are
HIGH (1), a LOW output (0) results.
Figure 26: XNOR Gate and its truth table
29

Schematic
Figure 27: Schematic of XNOR Gate
30

Waveforms
Figure 28: Waveform of XNOR Gate
RESULT
The wave forms of two input XNOR gate are obtained successfully.
31

11 EXPERIMENT NO.7
AIM
To design two input AND gate using two input NAND gate and inverter sym-
bols.
SOFTWARE REQUIRED
THEORY
Figure 29: Two input AND gate with truth table
A logic gate is an elementary building block of a digital circuit. A Logic
AND Gate is a type of digital logic gate that has an output which is normally
at logic level 0 and only goes high to a logic level 1 when all of its inputs are
at logic level 1. The output state of a Logic AND Gate only returns low again
when any of its inputs are at a logic level 0. In other words for a logic AND
gate, any low input will give a low output. The logic or Boolean expression
given for a logic AND gate is that for Logical Multiplication which is denoted
by a single dot or full stop symbol,( . ) giving us the Boolean expression of:
A.B = Output
Then we can deﬁne the operation of a 2-input logic AND gate as being:
If both A and B are true, then Output is true.
32

Design
For designing two input AND gate with CMOS logic ﬁrst we have to design
two input NAND gate and its output will be fed to a CMOS inverter to give the
output of AND gate as shown in the ﬁgure: Here the output of NAND gate say
Figure 30: AND gate using CMOS
Vz = Vx.Vy Then on passing it through the inverter gives out outputVf = Vx.Vy
which is the expression required for AND gate.
Schematic of NAND
Figure 31: Schematic of NAND gate
33

Schematic of NOT
Figure 32: Schematic of NOT gate
34

Schematic of AND
Figure 33: Schematic of AND gate
RESULT
Two input AND gate using two input NAND gate and Inverter symbols designed
successfully.
35

12 EXPERIMENT NO.8
AIM
To design S-R latch using symbol of NAND gate.
SOFTWARE REQUIRED
THEORY
A latch is a device with exactly two stable states. These states are high-output
and low-output. A latch has a feedback path, so information can be retained by
the device. Therefore latches can be memory devices, and can store one bit of
data for as long as the device is powered. Latches are very similar to flip-flops,
but are not synchronous devices, and do not operate on clock edges as flip-flops
do.
An SR latch (Set/Reset) is an asynchronous device: it works independently
of control signals and relies only on the state of the S and R inputs. SR latches
can be made from NAND gates. In this case, it is sometimes called an SR latch.
Figure 34: SR latch diagram with Function Table
36

Schematic of NAND Gate
Figure 35: Schematic of NAND Gate
Schematic(SYMBOL)
Figure 36: Schematic of Symbol of NAND Gate
37

Waveforms of NAND Gate
Figure 37: Waveform of NAND Gate
Schematic of SR Latch
Figure 38: Schematic of SR Latch
38

Waveforms of SR Latch
Figure 39: Waveform of SR latch
RESULT
S-R latch using symbol of NAND gate designed successfully.
39

13 EXPERIMENT NO.9
AIM
To design D flip flop using CMOS logic.
SOFTWARE REQUIRED
THEORY
The D flip-flop tracks the input, making transitions with match those of the input
D. The D stands for ”data”; this flip-flop stores the value that is on the data line.
It can be thought of as a basic memory cell. A D flip-flop can be made from a
set/reset flip-flop by tying the set to the reset through an inverter. D flip-flops
are by far the most common type of flip-flops and some devices (for example
some FPGAs) are made entirely from D flip-flops. They are also commonly
used for shift-registers and input synchronization.
Figure 40: Symbol and Truthtable of D flipflop
40

Schematic
Figure 41: Schematic D ﬂipﬂop
41

Waveforms
Figure 42: Waveform of D flipflop
RESULT
D flip flop using CMOS logic obtained successfully.
42

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